Microbial resource management of OLAND focused on sustainability

Several new biological nitrogen removal processes, which are based on partial nitritation/anammox, have been developed to treat nitrogen-rich wastewaters devoid in carbon such as digestates. Around 40 full-scale realizations of one-stage partial nitritation/anammox, in this work referred to as the oxygen-limited autotrophic nitrification/denitrification (OLAND) process, are operational at this moment for high strength nitrogen streams. OLAND is based on partial nitritation, performed by aerobic ammonium-oxidizing bacteria (AerAOB) and anammox, performed by anoxic ammonium-oxidizing bacteria (AnAOB). The AerAOB, mainly belonging to Nitrosomonas europaea eutropha and halophila, are set so that they oxidize half of the influent ammonium to nitrite in oxygen-limited conditions. The AnAOB, mainly members of the Candidatus genera Kuenenia and Brocadia, oxidize the residual ammonium with nitrite to dinitrogen gas under anoxic conditions. Consequently, in the OLAND process ammonium is converted mainly into nitrogen gas without the use of organic carbon in one reactor. Overall OLAND can save 84% of the operational costs, by a 100, 89 and 57% decrease in methanol requirement, sludge production and aeration, respectively.
The close interaction between the different microbial groups during the OLAND process is comparable with human beings working together in firms for a shared profit. In this sense, the concept of human resource management (HRM) was translated to the microbial biotechnology as Microbial Resource Management (MRM) and therefore strives after maintaining the best performing microbial community for a certain application. A MRM OLAND framework was elaborated (Chapter 1), showing how the OLAND engineer/operator (1: input) can design/steer the microbial community (2: biocatalyst) to obtain optimal functionality (3: output), depending on the application domain (0: wastewater). Taken this MRM framework into account, the OLAND engineer can steer the OLAND process to obtain maximum efficiency and higher sustainability or to increase the impact of OLAND on the energy balance of wastewater treatment plants (WWTP).
Although the first OLAND applications have shown that this technology works in a stable and efficient way, the implementation rate of this technology remains dependent on a few companies. Many potential users hold back because it seems that due to the long start-up periods for the first reactors and the reported sensitivities, a lot of experience is needed to keep this process running. To overcome this problem, the output box of the MRM framework was further studied in detail for high-strength nitrogen containing wastewaters (known application). Firstly, the effect of the hydraulic conditions on the start-up of the OLAND sequencing batch reactor (SBR) was examined. Low volumetric exchange ratios, which assure stable hydraulic conditions, were needed to allow a fast start-up, granulation and high performance in SBR systems (Chapter 2). Furthermore, strategies to obtain a well-balanced OLAND system, were proposed based on wash-out of nitrite oxidizing bacteria (NOB) through selection on settling velocity or by stimulation of AnAOB through the implementation of an anoxic phase. As not only the effluent quality, but also the sustainability can be a competitive factor to choose an environmental technology, the N2O and NO emissions were studied in a full-scale OLAND-type reactor (Chapter 3). The sustainability of the process in terms of NO/N2O emissions was mainly linked with accumulations of intermediates such as NO2- and NH2OH and the frequency of transient conditions. Better understanding of the conditions which lead to the accumulation of intermediates and further optimization of the feeding pattern which determines the degree of fluctuations, will allow a further decrease of the N2O emission in these systems.
In a next part of this work, new opportunities for OLAND, which could improve the overall sustainability of the applied processes, were explored (box 0 of MRM framework). Energy calculations revealed that OLAND treatment of digestates could significantly increase the energy index of agro-industrial and organic fraction of municipal solid waste-based treatment system from 3-5 to 6-10 (Chapter 4). However, for manure-based digestate treatment, OLAND application seemed more difficult and therefore ammonia gas treatment by OLAND was suggested for this application domain. A pilot-scale OLAND biofilter fed with a flow of ammonia gas, obtained a high performance (0.7 g N L-1 d-1) and a high total nitrogen removal efficiency (75-80%; Chapter 5). Although the filter was saturated with oxygen, the low relative water flow rate ratio (≈1 L g-1 Nin) ensured high free ammonia concentration in the water phase, which resulted in a dominance of AnAOB compared to NOB activity at the top of the biofilter.
A specific application domain, which could particularly improve the energy efficiency of sewage treatment plants was the implementation of OLAND in the mainstream of the system. This would allow a net electrical energy production, due to a higher carbon recovery and lower energy needs for aeration (Chapter 4). Four challenges to allow mainstream OLAND were encountered. A first challenge, namely the performance of OLAND at low nitrogen concentration and low hydraulic residence time (HRT) was shown in an OLAND rotating biological contactor (RBC; Chapter 6). The reactor obtained high nitrogen removal rates (0.4 g N L-1 d-1) treating nitrogen concentration of 30-60 mg N L-1 at a HRT of 1-2 hours. A second challenge, operation at low temperatures (15°C), was surmounted in the same RBC by gradually decreasing the temperature starting from 29°C. During operation at 15°C with synthetic feed (60 mg N L-1) and a HRT of 1h, a similar nitrogen removal rate as at high temperatures was obtained i.e. 0.5 g N L-1 d-1 (Chapter 7). Compared to higher temperatures only a decrease of the total removal efficiency of 22% was detected. The switch from synthetic feed to pretreated sewage with a COD/N ratio of 2 (challenge 3) did not significantly affect the performance. However, during the low temperature performance of the RBC system, NOB activity started to increase, as well as competition between AnAOB and NOB for nitrite (challenge 4). It was shown that increased levels of NO selectively enhanced AnAOB over NOB activity (Chapter 7). Therefore, high peak loading rates together with nitrite accumulation, increasing the NO production, enhanced the overall removal efficiency. To evaluate the mainstream OLAND application in a broader context, a life cycle assessment (LCA) was performed on full-scale data of the WWTP in Strass, which applied an OLAND-type of system, referred to as DEMON. Three scenarios were studied: (1) the WWTP without a DEMON system; (2) the WWTP with DEMON in the side line; (3) the WWTP with DEMON in the side and main lines (Chapter 8). For the latter scenario, data from a first full-scale trial were used. The LCA showed that implementation of DEMON in the side line of the WWTP positively influenced the eutrophication potential, abiotic depletion potential and global warming potential and therefore resulted in a more sustainable WWTP. The first full-scale results of DEMON implementation in the mainstream of the WWTP in Strass (Austria) showed that to obtain the same degree of sustainability compared to the WWTP with sidestream treatment, the N2O emission (around 2% of N load) in the main line should be decreased as this compound dominated the global warming potential of the plant with 99%. N2O emission is mainly related with operational conditions and not with the process itself, it should therefore be possible to further optimize the emission to around 0.5% of the N load allowing the same CO2 footprint of the plant in comparison with sidestream OLAND implementation.
Generally, this work showed that new potential domains for OLAND were located in agricultural applications requiring ammonia gas removal and in municipal WWTP using mainstream treatment. Future tests in these domains will need to evaluate the performance and overall environmental sustainability at larger scale.

@phdthesis{3032231,
abstract = {Several new biological nitrogen removal processes, which are based on partial nitritation/anammox, have been developed to treat nitrogen-rich wastewaters devoid in carbon such as digestates. Around 40 full-scale realizations of one-stage partial nitritation/anammox, in this work referred to as the oxygen-limited autotrophic nitrification/denitrification (OLAND) process, are operational at this moment for high strength nitrogen streams. OLAND is based on partial nitritation, performed by aerobic ammonium-oxidizing bacteria (AerAOB) and anammox, performed by anoxic ammonium-oxidizing bacteria (AnAOB). The AerAOB, mainly belonging to Nitrosomonas europaea eutropha and halophila, are set so that they oxidize half of the influent ammonium to nitrite in oxygen-limited conditions. The AnAOB, mainly members of the Candidatus genera Kuenenia and Brocadia, oxidize the residual ammonium with nitrite to dinitrogen gas under anoxic conditions. Consequently, in the OLAND process ammonium is converted mainly into nitrogen gas without the use of organic carbon in one reactor. Overall OLAND can save 84\% of the operational costs, by a 100, 89 and 57\% decrease in methanol requirement, sludge production and aeration, respectively.
The close interaction between the different microbial groups during the OLAND process is comparable with human beings working together in firms for a shared profit. In this sense, the concept of human resource management (HRM) was translated to the microbial biotechnology as Microbial Resource Management (MRM) and therefore strives after maintaining the best performing microbial community for a certain application. A MRM OLAND framework was elaborated (Chapter 1), showing how the OLAND engineer/operator (1: input) can design/steer the microbial community (2: biocatalyst) to obtain optimal functionality (3: output), depending on the application domain (0: wastewater). Taken this MRM framework into account, the OLAND engineer can steer the OLAND process to obtain maximum efficiency and higher sustainability or to increase the impact of OLAND on the energy balance of wastewater treatment plants (WWTP).
Although the first OLAND applications have shown that this technology works in a stable and efficient way, the implementation rate of this technology remains dependent on a few companies. Many potential users hold back because it seems that due to the long start-up periods for the first reactors and the reported sensitivities, a lot of experience is needed to keep this process running. To overcome this problem, the output box of the MRM framework was further studied in detail for high-strength nitrogen containing wastewaters (known application). Firstly, the effect of the hydraulic conditions on the start-up of the OLAND sequencing batch reactor (SBR) was examined. Low volumetric exchange ratios, which assure stable hydraulic conditions, were needed to allow a fast start-up, granulation and high performance in SBR systems (Chapter 2). Furthermore, strategies to obtain a well-balanced OLAND system, were proposed based on wash-out of nitrite oxidizing bacteria (NOB) through selection on settling velocity or by stimulation of AnAOB through the implementation of an anoxic phase. As not only the effluent quality, but also the sustainability can be a competitive factor to choose an environmental technology, the N2O and NO emissions were studied in a full-scale OLAND-type reactor (Chapter 3). The sustainability of the process in terms of NO/N2O emissions was mainly linked with accumulations of intermediates such as NO2- and NH2OH and the frequency of transient conditions. Better understanding of the conditions which lead to the accumulation of intermediates and further optimization of the feeding pattern which determines the degree of fluctuations, will allow a further decrease of the N2O emission in these systems.
In a next part of this work, new opportunities for OLAND, which could improve the overall sustainability of the applied processes, were explored (box 0 of MRM framework). Energy calculations revealed that OLAND treatment of digestates could significantly increase the energy index of agro-industrial and organic fraction of municipal solid waste-based treatment system from 3-5 to 6-10 (Chapter 4). However, for manure-based digestate treatment, OLAND application seemed more difficult and therefore ammonia gas treatment by OLAND was suggested for this application domain. A pilot-scale OLAND biofilter fed with a flow of ammonia gas, obtained a high performance (0.7 g N L-1 d-1) and a high total nitrogen removal efficiency (75-80\%; Chapter 5). Although the filter was saturated with oxygen, the low relative water flow rate ratio (\ensuremath{\asymp}1 L g-1 Nin) ensured high free ammonia concentration in the water phase, which resulted in a dominance of AnAOB compared to NOB activity at the top of the biofilter.
A specific application domain, which could particularly improve the energy efficiency of sewage treatment plants was the implementation of OLAND in the mainstream of the system. This would allow a net electrical energy production, due to a higher carbon recovery and lower energy needs for aeration (Chapter 4). Four challenges to allow mainstream OLAND were encountered. A first challenge, namely the performance of OLAND at low nitrogen concentration and low hydraulic residence time (HRT) was shown in an OLAND rotating biological contactor (RBC; Chapter 6). The reactor obtained high nitrogen removal rates (0.4 g N L-1 d-1) treating nitrogen concentration of 30-60 mg N L-1 at a HRT of 1-2 hours. A second challenge, operation at low temperatures (15{\textdegree}C), was surmounted in the same RBC by gradually decreasing the temperature starting from 29{\textdegree}C. During operation at 15{\textdegree}C with synthetic feed (60 mg N L-1) and a HRT of 1h, a similar nitrogen removal rate as at high temperatures was obtained i.e. 0.5 g N L-1 d-1 (Chapter 7). Compared to higher temperatures only a decrease of the total removal efficiency of 22\% was detected. The switch from synthetic feed to pretreated sewage with a COD/N ratio of 2 (challenge 3) did not significantly affect the performance. However, during the low temperature performance of the RBC system, NOB activity started to increase, as well as competition between AnAOB and NOB for nitrite (challenge 4). It was shown that increased levels of NO selectively enhanced AnAOB over NOB activity (Chapter 7). Therefore, high peak loading rates together with nitrite accumulation, increasing the NO production, enhanced the overall removal efficiency. To evaluate the mainstream OLAND application in a broader context, a life cycle assessment (LCA) was performed on full-scale data of the WWTP in Strass, which applied an OLAND-type of system, referred to as DEMON. Three scenarios were studied: (1) the WWTP without a DEMON system; (2) the WWTP with DEMON in the side line; (3) the WWTP with DEMON in the side and main lines (Chapter 8). For the latter scenario, data from a first full-scale trial were used. The LCA showed that implementation of DEMON in the side line of the WWTP positively influenced the eutrophication potential, abiotic depletion potential and global warming potential and therefore resulted in a more sustainable WWTP. The first full-scale results of DEMON implementation in the mainstream of the WWTP in Strass (Austria) showed that to obtain the same degree of sustainability compared to the WWTP with sidestream treatment, the N2O emission (around 2\% of N load) in the main line should be decreased as this compound dominated the global warming potential of the plant with 99\%. N2O emission is mainly related with operational conditions and not with the process itself, it should therefore be possible to further optimize the emission to around 0.5\% of the N load allowing the same CO2 footprint of the plant in comparison with sidestream OLAND implementation.
Generally, this work showed that new potential domains for OLAND were located in agricultural applications requiring ammonia gas removal and in municipal WWTP using mainstream treatment. Future tests in these domains will need to evaluate the performance and overall environmental sustainability at larger scale.},
author = {De Clippeleir, Hayd{\'e}e},
isbn = {9789059895515},
keyword = {anammox,nitrogen,autotrophic nitrogen removal,OLAND,energy},
language = {eng},
pages = {VII, 217},
publisher = {Ghent University. Faculty of Bioscience Engineering},
school = {Ghent University},
title = {Microbial resource management of OLAND focused on sustainability},
year = {2012},
}